A hybrid vehicle using a high voltage battery has a system for automatically cutting off power of the main high voltage battery in an emergency. The emergency refers to an excessive short circuit due to obsolescence of relevant components, an excessive short circuit caused by a short stemming from a breakdown of components due to a dielectric breakdown, etc., and an external impact, a dielectric breakdown, or the like.
In case of an emergency in a vehicle, an upper component which controls high voltage components such as a battery management system (BMS), a hybrid control unit (HCU), or the like, issues a command for cutting off a main power source to regulate power. For the high voltage-related components, voltages and currents of a line connecting a power source are monitored through an array of programs or sensors, and when a voltage and a current which are not within a normal range are detected, when there is a leakage current greater than an allowable value, or when there is an insulation resistance breakdown greater than an allowable value, or the like, the main power source is cut off by CAN communication or a signal transmission.
In this manner, the measurement of insulation resistance is very important in the hybrid vehicle using a high voltage battery. One of methods for measuring a leakage current between the high voltage battery and the hybrid vehicle is breaking down insulation and forcibly making a DC current flow, but this method is disadvantageous in that insulation is broken down while insulation resistance is being measured.
Thus, in order to solve this problem, a coupling condenser is connected between the high voltage battery and the hybrid vehicle and an AC signal is applied to the coupling condenser to measure an insulation resistance component. However, this method has shortcomings in that it has a great amount of restrictions in designing a circuit because a current for charging the coupling condenser and a current for discharging the coupling condenser must pass through the same circuit.
Therefore, a development of a small, light-weight, and low-priced insulation resistance measurement circuit capable of simply and precisely measuring insulation resistance between a chassis ground and a high voltage battery of a hybrid vehicle is required.